The subject matter of this disclosure generally relates to optical computing devices and, more particularly, to birefringent optical elements configured for use in optical computing devices.
Optical computing devices, also commonly referred to as “opticoanalytical devices,” can be used to analyze and monitor a substance in real time. Such optical computing devices will often employ an optical processing element that optically interacts with the substance or a sample thereof to determine quantitative and/or qualitative values of one or more physical or chemical properties of the substance. The optical element may be, for example, an integrated computational element (ICE), also known as a multivariate optical element (MOE), which includes an optical interference filter that can be designed to operate over a continuum of wavelengths in the electromagnetic spectrum from the ultraviolet (UV) to mid-infrared (MIR) ranges, or any sub-set of that region. Electromagnetic radiation that optically interacts with the ICE is changed so as to be readable by a detector, such that an output of the detector can be correlated to a physical or chemical property of the substance being analyzed.
An ICE (hereafter “ICE component”) typically includes a plurality of optical layers that include various materials whose index of refraction and size (e.g., thickness) may vary between each layer. An ICE design refers to the number and thickness of the respective layers of the ICE component. The layers may be strategically deposited and sized so as to selectively pass predetermined fractions of electromagnetic radiation at different wavelengths, being configured to substantially mimic a regression vector corresponding to a particular physical or chemical property of interest of a substance. Accordingly, an ICE design will exhibit a transmission function that is weighted with respect to wavelength. As a result, the output light intensity from the ICE component conveyed to the detector may be related to the physical or chemical property of interest for the substance.
To date, the several layers that make up the ICE component are typically made from isotropic materials, or materials whose refractive indices are independent of the polarization state or the direction vectors of light propagating through them.